Hearing loss in dogs, as in humans, can be caused by a wide range of disease, trauma, and/or congenital problems. In congenital cases, the dog is born deaf. Hearing loss can come on suddenly or gradually due to injury, disease, ear infections, exposure to loud noises or explosions, or simply the wear and tear of old age.

Hearing loss is categorized as unilateral (affecting one ear only) or bilateral (affecting both ears). Dogs with white or partially white coats are often subject to a congenital form of deafness connected with the special pigmentation in their skin. In these cases the dog may have unpigmented skin in the inner ear, which causes the nerve endings inside the ear to wither away and die when the affected puppy is only a few weeks old. The end result is deafness.

Unlike some conditions, hearing problems are usually noticeable to the pet owner. Dogs with congenital deafness will show symptoms early, usually before the puppy has been weaned. One sign may be a pup that bites its littermates too aggressively while playing, since it can't hear the others' yelps of pain. Once in your home, the dog also may bite too hard when playing with the family for the same reason. More often, the animal simply won't come when called or is otherwise unresponsive to noises in its vicinity. (Deaf dogs that are too aggressive can be trained to develop what's called a "soft mouth.")

The only certain way to test your dog's hearing is through a BAER test. The acronym stands for "Brainstem Auditory Evoked Response." The test itself is a computer-assisted program that records the electrical activity in the dog's brain in response to a variety of sound stimulations. It's the same test used to measure hearing in human infants, and it measures the same range of hearing. It doesn't test the full range of a dog's hearing, though, and there are some cases in which a dog will be unable to hear noises heard by a human, but will still be able to hear some high pitches, such as a dog whistle. The BAER test is not painful, and it can be performed on any animal over six weeks old.

Since BAER testing can be expensive and is not available at every veterinary practice, some owners opt to assess their dog's hearing at home or more informally, with their vet's assistance. You can check your dog's hearing at home with the following actions:

Call your dog in a normal voice. If it doesn't respond, try yelling.

Whistle or blow a whistle and note the dog's response.

Squeak a toy behind your back.

Jangle car keys or a can of coins.

Have someone ring your doorbell.

Clap your hands. (Be sure to be far enough away that the dog does not feel any air movement.)

Owners performing these tests will get a variety of responses, depending upon whether the dog is entirely or partially deaf in one or both ears. It's advised you try a variety of sounds, because as hearing erodes, dogs may lose either the upper or lower portion of the audio spectrum.

There is no effective treatment for deafness in canines, but most dogs adjust very well to their limitations. Many dogs also can be trained to respond to hand or light signals as well.